In control systems including a control unit and a plurality of controlled devices, so-called wiring saving of reducing the number of wires has been widely performed. As a general technique for wiring saving, a technique of connecting a master station with a function of performing conversion between a parallel signal and a serial signal and a plurality of slave stations with a control unit and a controlled device, respectively, and performing data transfer between the master station and the plurality of slave stations via a common data signal line using a serial signal, instead of a parallel connection of connecting each of signal lines extending from a plurality of controlled devices directly to a control unit has been widely employed.
In the case in which wiring saving is implemented, when it is difficult for a control unit side to identify a low sensitivity state of a signal of an input unit in a slave station in a state in which a number of slave stations are connected, it is necessary to check each of the slave stations far away from the control unit, and thus it requires many man-hours to detect the low sensitivity state of the signal of the input unit in the slave station.
In this regard, the present inventors have considered applying a remote wiring check system disclosed in JP 2011-114449 A as a system in which a low sensitivity state of a signal of an input unit in a slave station is identified at a control unit. In this remote wiring check system, a control/monitoring signal transmission system includes a single control unit and a plurality of controlled devices. In the system, a management data region includes connection data indicating a wiring state which is different from a control/monitoring data region including control data (output data) and monitoring data (input data) which are bidirectionally and simultaneously transmitted between a master station and a slave station connected via a wiring-saved data signal line. In the connection data, short circuit information, disconnection information, and normality information are identified. Thus, it is possible to easily check the wiring connection state of the slave station without reducing input data (monitoring data) capacity of a signal.
Further, JP 2006-331449 A discloses a slave (slave station) having a function of acquiring start time information when an ON state or an OFF state of an OUT terminal connected with an output device (output unit) has changed by OUT data received through serial communication with a master unit (master station), a function of acquiring stop time information when an ON state or an OFF state of an IN terminal connected with an input device (input unit) has changed, and a calculation function of calculating an operation period of time of the output device based on the start time information and the stop time information. According to this slave (slave station), it is possible to determine whether the output device or the input device is in the normal state, whether a replacement time has approached, or the like by obtaining the operation period of time of the output device or the input device and comparing the obtained operation period of time with setting information used for identifying a normal range of the output device or the input device.